Iran's chief nuclear negotiator Saeed Jalili arrived in Moscow Sunday for critical talks with world powers, flying economy class with his team on Russia's state airline, Aeroflot.

Mr. Jalili projects a "common man" image, but upon his shoulders may rest the high-stakes result of the third round of nuclear talks which begins Monday in Moscow.

Expectations are low that Iran and the P5+1 group – the United States, Russia, China, Britain, France and Germany – will be able to strike a deal that at once would permanently prevent Iran's push for an atomic bomb and preserve for Tehran most of its advanced nuclear program.

Hopes raised in Istanbul in April were set back in Baghdad in May, when the P5+1 initial proposal demanded more concessions than Iran expected. It required Iran to suspend all uranium enrichment and give up entirely on higher-level enrichment, with no immediate easing of tough economic sanctions.

Since then, acrimonious exchanges and demands by politicians opposed to compromise in both the U.S. and Iran have made a breakthrough here even less likely.

Iranian diplomats charge that the P5+1 offer violated the framework agreed in Istanbul of a reciprocal, step-by-step exchange of concessions. P5+1 officials counter that Iran must first agree to take "concrete" action in Moscow.

But analysts say Iran's perception that it is being forced to accept a lopsided offer is unacceptable to the psychology of its leadership – and risks a collapse of the talks that could lead to military strikes by Israel or the U.S.

"You have this classic case of asymmetry," said John Limbert, a veteran diplomat who was U.S. Deputy Assistant Secretary of State for Iran until 2010.

"We're talking about one thing, all these legal and technical issues, and the Iranians are talking about their place in the world, their rights, their sovereignty. We just talk past each other. And both sides come away saying, 'They are not listening to us.'"

EU foreign policy chief Catherine Ashton represents the P5+1 at the table. U.S. Undersecretary of State for Political Affairs Wendy Sherman is also there with other senior P5+1 officials.

For any deal to stick, both sides need to be able to sell it at home as their own victory, and that impulse for Iran was clear when Jalili briefed the Parliament last week. The Moscow talks would proceed under the framework of the Nuclear Non-Proliferation Treaty, which describes an "inalienable right" of nations to produce nuclear energy.

There was "no prohibition" of "any kind of enrichment for peaceful purposes," Jalili told the chamber. "It's possible that we may need higher or lower enrichment for other peaceful applications. This is our right, and we must be able to exercise this right."

Several UN Security Council resolutions require Iran to suspend all enrichment, however, until it resolves questions about past weapons-related work.

Iranian officials have stated a readiness to deal on their 20 percent enriched uranium, which is a few technical steps from weapons grade of more than 90 percent.

But giving up all enrichment, they say, will not happen. And for any deal, Iran expects something it values in return, like relief from harsh U.S. and European economic sanctions.

"All sides need to be courageous enough to recognize a fair exchange is a central tenet of dialogue."

The P5+1 proposal includes stopping 20 percent enrichment and shutting down a deeply buried enrichment site where it happens at Fordow, which is currently under safeguard by UN nuclear inspectors but beyond easy reach of Israeli or US attack.

"The offer was deliberately ungenerous – some would say unrealistic" and probably an opening bid, the International Crisis Group think tank noted in a report last Friday.

A U.S. official told ICG that "the burden of proof is on the Iranians. They are the ones running an illicit nuclear program. We will engage in a step-by-step process, but our actions are not necessarily going to be equivalent to theirs."

P5+1 diplomats frequently cite increasingly painful sanctions – with further measures against Iran's central bank and a European oil embargo due at the end of this month – as the reason Iran is at the table. Iran denies that.

"History shows that pushing Iran into a corner will backfire," said Kayhan Barzegar, director of the Institute for Middle East Strategic Studies in Tehran. The strategically important and widely supported nature of Iran's nuclear program means Iran can "easily resist against increased pressures."

"A win-win solution is inevitable. The other option is a lose-lose situation."

Iran says it takes the P5+1 strategy that hardened considerably between the Istanbul and Baghdad talks, as a red flag about Western seriousness to make a deal.

Barzegar said this hardening has stirred up "distrust among Iranian decision-makers" and "strengthen(ed) the hard-line view that Iran is only wasting its time (with talks) and that the main goal of the West is to bring the (nuclear) program to a complete halt."

Indeed, Iran's parliament speaker Ali Larijani said last week that the negotiating team "has no right to show leniency," and that Iran would determine its own enrichment levels – an indirect reference to 20 percent, according to Mehr News Agency.

Parliament expected negotiators in Moscow to "consolidate what the Iranian nation has gained after years," said Larijani.

A group of senators in Washington likewise sought to shape the talks, with nearly half sending a letter to President Barack Obama on Friday demanding an "absolute minimum" of immediate concessions by Iran in Moscow – halting 20 percent enrichment, and closing Fordow – if talks were to continue.

The 44 senators asked Mr. Obama not to ease sanctions, which needed to be "unremitting and crippling," and to boost pressure on Iran by "making clear that a credible military option exists."

"The idea of what we should be getting, and what we should be giving, on both sides, is completely at odds," said Eskandar Sadeghi-Boroujerdi, a doctoral candidate at Oxford University and lead writer of a recent Oxford Research Group study on breaking the nuclear deadlock.

Increasing sanctions may have helped bring Iran to the table, but they can also become a trap, he said.

"Once you get into this frame of mind, where you have to have sanctions and they keep piling up, it's very difficult to reverse it. There has to be a balanced advantage in every phase, so each side starts to feel, 'We've got something which is worth what we are giving'. Calibrating that is quite tricky, (even when) there is a will on both sides. We're not seeing it enough."